集合——Dictionary



集合——Dictionary<K,V>

Dictionary 泛型類有兩個類型參數，而 List 中只有一個。Dirctionary<K,V>，其中 K 代表字典中鍵個類型，V 代表字典中值的類型。字典中用一個鍵對應一個值，鍵和值存在這種一一映射的關係，檢索速度取決於爲 K 指定的類型的哈希算法的質量。常用的方法與 List 類似，但是需要分別使用 Keys 屬性和 Values 屬性單獨枚舉鍵和值。

Dictionary 成員參見： msdn.microsoft.com/zh-cn/library/3eayzh46(VS.80).aspx

看下面的例子：

1. using System;   
2. using System.Collections.Generic;   
3.   
4. public class Example   
5. {   
6.     public static void Main()   
7.      {   
8.         // 使用 string 類型建立字典的鍵和值   
9.          Dictionary<string, string> openWith =   
10.             new Dictionary<string, string>();   
11.   
12.         // 添加一些元素給鍵和值，鍵是不可重複的，而值可以重複。   
13.          openWith.Add("txt", "notepad.exe");   
14.          openWith.Add("bmp", "paint.exe");   
15.          openWith.Add("dib", "paint.exe");   
16.          openWith.Add("rtf", "wordpad.exe");   
17.   
18.         // 捕獲字典中存在相同的鍵而產生的異常   
19.         try  
20.          {   
21.              openWith.Add("txt", "winword.exe");   
22.          }   
23.         catch (ArgumentException)   
24.          {   
25.              Console.WriteLine("An element with Key = \"txt\" already exists.");   
26.          }   
27.   
28.         // 可以使用鍵名作爲索引取出對應的值   
29.          Console.WriteLine("For key = \"rtf\", value = {0}.",   
30.              openWith["rtf"]);   
31.   
32.         // 也可以通過鍵名索引改變對應的值   
33.          openWith["rtf"] = "winword.exe";   
34.          Console.WriteLine("For key = \"rtf\", value = {0}.",   
35.              openWith["rtf"]);   
36.   
37.         // 如果鍵名是不存在的，將會自動添加到字典   
38.          openWith["doc"] = "winword.exe";   
39.   
40.         // 捕獲不存在的鍵名   
41.         try  
42.          {   
43.              Console.WriteLine("For key = \"tif\", value = {0}.",   
44.                  openWith["tif"]);   
45.          }   
46.         catch (KeyNotFoundException)   
47.          {   
48.              Console.WriteLine("Key = \"tif\" is not found.");   
49.          }   
50.   
51.         // 用TryGetValue方法測試一個鍵是否存在，若存在就顯示出來   
52.         string value = "";   
53.         if (openWith.TryGetValue("tif", out value))   
54.          {   
55.              Console.WriteLine("For key = \"tif\", value = {0}.", value);   
56.          }   
57.         else  
58.          {   
59.              Console.WriteLine("Key = \"tif\" is not found.");   
60.          }   
61.   
62.         // 通常我們在添加新鍵前使用ContainsKey方法   
63.         if (!openWith.ContainsKey("ht"))   
64.          {   
65.              openWith.Add("ht", "hypertrm.exe");   
66.              Console.WriteLine("Value added for key = \"ht\": {0}",   
67.                  openWith["ht"]);   
68.          }   
69.   
70.         // 使用foreach加KeyValuePair方法得到所有元素   
71.          Console.WriteLine();   
72.         foreach( KeyValuePair<string, string> kvp in openWith )   
73.          {   
74.              Console.WriteLine("Key = {0}, Value = {1}",   
75.                  kvp.Key, kvp.Value);   
76.          }   
77.   
78.         // 獲得值集合   
79.          Dictionary<string, string>.ValueCollection valueColl =   
80.              openWith.Values;   
81.   
82.         // 使用foreach枚舉所有值   
83.          Console.WriteLine();   
84.         foreach( string s in valueColl )   
85.          {   
86.              Console.WriteLine("Value = {0}", s);   
87.          }   
88.   
89.         // 獲得鍵集合   
90.          Dictionary<string, string>.KeyCollection keyColl =   
91.              openWith.Keys;   
92.   
93.         // 使用foreach枚舉所有鍵   
94.          Console.WriteLine();   
95.         foreach( string s in keyColl )   
96.          {   
97.              Console.WriteLine("Key = {0}", s);   
98.          }   
99.   
100.         // Remove方法刪除元素   
101.          Console.WriteLine("\nRemove(\"doc\")");   
102.          openWith.Remove("doc");   
103.   
104.         if (!openWith.ContainsKey("doc"))   
105.          {   
106.              Console.WriteLine("Key \"doc\" is not found.");   
107.          }   
108.   
109.          Console.Write("\nPress any key to exit...");   
110.          Console.ReadKey();   
111.      }   
112. }   
113.   
114. /* 運行結果:
116. An element with Key = "txt" already exists.
117. For key = "rtf", value = wordpad.exe.
118. For key = "rtf", value = winword.exe.
119. Key = "tif" is not found.
120. Key = "tif" is not found.
121. Value added for key = "ht": hypertrm.exe
123. Key = txt, Value = notepad.exe
124. Key = bmp, Value = paint.exe
125. Key = dib, Value = paint.exe
126. Key = rtf, Value = winword.exe
127. Key = doc, Value = winword.exe
128. Key = ht, Value = hypertrm.exe
130. Value = notepad.exe
131. Value = paint.exe
132. Value = paint.exe
133. Value = winword.exe
134. Value = winword.exe
135. Value = hypertrm.exe
137. Key = txt
138. Key = bmp
139. Key = dib
140. Key = rtf
141. Key = doc
142. Key = ht
144. Remove("doc")
145. Key "doc" is not found.
146. */